The present invention relates to a system and method for regulating the load on an engine-driven apparatus.
For example, an engine-driven tractor having a lifting mechanism is capable of carrying out various operations such as ploughing, harrowing, trailer towing, towing a combine drill, and other equivalent operations Other operations performed by an engine driven apparatus such as a tractor are pulling or pushing a prime mover and carrying out tasks in municipal service soil engineering and peat milling.
In performing work of the above general type there is as a general rule a certain dominating factor. For example such a dominating factor is the ploughing depth when performing ploughing operations, a given supporting force or a given pressure in the power cylinder of the lifting mechanism when a combine drill is towed, the brushing depth or brushing pressure against the surface in street repair work, the milling depth in peat milling, etc. It is highly advantageous when carrying out practical operations of the above type to maintain this dominating factor substantially constant. For a number of different reasons, however, when operations of the above type are carried out certain variables which reflect the operating condition of the tractor or disturbance thereof, such as slip and overloading of the engine, should be eliminated, so that it is necessary to make certain concessions in stabilizing such a dominating factor, and in addition it is necessary to govern such operations as the hydrostatic power transmission and/or the differential drive lock automatically in order to have the work proceed smoothly.
In tractors and other types of apparatus driven by engines such as diesel engines, such engines include a fuel injection pump which forms part of the engine-speed control mechanism. For example, the operator of a tractor has control over a speed-control lever by means of which the operator may set the desired speed. If as a result of an increase in the external load such as in increase in the resistance encountered by a plough, there is a load on the engine which exceeds the maximum torque consistent with the desired engine speed, then the fuel injection of the engine can no longer increase and instead the engine speed falls off. At this point the driver should shift to a lower gear or take other steps in order to reduce the external load so as to prevent stopping of the work.
It is already known to provide measures intended to alleviate problems of the above type. However, the known expedients suffer from serious drawbacks such as simply limiting the maximum fuel which can be delivered to the engine without controlling the load or if the load is automatically regulated the arrangements provided for this purpose are exceedingly complex and expensive.